Recently, there is a rapid trend for smaller size, lighter weight, thinner structure, and multiple functions for electronic appliances, and various technologies for mounting circuit elements at high density are proposed. One of them is a technology for embedding electronic components in a substrate.
As this type of substrate embedding electronic components, for example, Japanese Laid-open Patent No 63-169798 is known, and the structure as shown in FIG. 12(a) realizes an equivalent circuit as shown in FIG. 12(b).
In the diagram, reference numeral 102 denotes a multi-layer substrate laminating ceramic substrates 121 through 126 in multiple layers. Capacitors 103, 104 and resistor 105 are inserted in penetration holes 107 formed in multi-layer substrate 102, and they are electrically connected by conductors 106.
In the prior art, however, capacitors 103, 104 and resistor 105 must be finally baked together with multi-layer substrate 102, and special components excellent in heat resistance are needed. But it is hard to obtain sufficient heat resisting effect as the size of the electronic components becomes smaller. Specified values may not be obtained due to characteristic deterioration or characteristic fluctuation by heat treatment at high temperature, and therefore, desired circuit characteristics and functions are not obtainable. The dimensions vary due to shrinkage and contraction by heat treatment at high temperature, and it is accordingly hard to obtain components of precise dimensions, and size reduction is limited.